The present invention relates to a process and device for the detection of pathogens, such as bacteria, fungi and viruses, in blood.
Today, septic complications are one of the chief causes of death of patients who are in intensive care units because of an otherwise serious illness. The causes are the weakened resistance to infection due to the fundamental disease and the inability completely to prevent infection by pathogens from other patients.
Today, more than 60 antiobiotics from 13 different groups of preparations provide the possibility of taking positive action against diagnosed pathogens. An early diagnosis and thus an improved possibility of therapy can decisively improve the chances of survival of patients suffering from a bacterial or mycotic attack of the system.
Diagnosis of sepsis is provided by the clinical picture (fever, shivering, leukocytosis, leftward shift in the differential blood picture and consumption coagulopathy, as well as septic shock and other non-specific signs) and from the cultured detection of micro-organisms in the blood of the patient. In the case of a positive detection of micro-organisms, the antibiogram also gives important indications for the most effective antibiotic or antimycotic therapy. The bacteriological detection processes which are today conventional are essentially only technical variants of the blood culture techniques developed at the turn of the century. By means of the introduction of the liquoid venules and of the blood culture bottle with previously prepared nutrient substrate, a relative optimization of the well-known processes was achieved. However, for clinical purposes, the results obtained with these processes are still not satisfactory. The previous improvements of the blood culture processes were limited to the development of more sensitive bacteriological detection techniques. This applies not only to the radiometric measurement of marked carbon dioxide but also to membrane filtration methods and the further developments thereof.
The chance of being able to identify pathogens with the conventional blood sampling techniques for culture purposes is only 30% of all clinically certain cases, which is terribly low. This low quotient of success could, according to present day knowledge, have two causes:
1. The septic focus does not emit a continuous stream of pathogens but rather an intermittent one. The ideal point of time to obtain the pathogens from the blood circulation is prior to the appearance of clinical symptoms, such as fever and shivering. PA1 2. A large number of patients is already treated with antibiotics. These antibiotics unavoidably pass with the pathogen into the culture medium and suppress the growth of the micro-organisms so that the blood culture can give a falsely negative result. This means that in 70% of all cases of clinically certain sepsis, the fight is against unknown pathogens and usually also without knowing whether it is a bacterial or a fungal sepsis. Thus, the choice of the correct anti-biotic or anti-mycotic is purely a matter of luck.
For years, attempts have been made to close this diagnostic loophole. New methods have been developed which are supposed to give a quicker and more certain detection of pathogens in the blood than the previously known processes. However, even in the case of these new processes, three decisive disadvantages still remain. The blood sample must still be collected at the precise point of time at which the pathogens pass into the circulation and thus, in the ideal case, before the patient shows an increase in temperature. Furthermore, only a small aliquot from the total amount of blood is used for the investigation. In the case of patients who have been previously treated with antibiotics, residues of antiobiotics are also introduced into the culture and there bring about an inhibition of the growth of the pathogens.